This invention relates to inkjet printing devices, and more particularly to an inkjet printing device that includes a printhead portion that receives drop activation signals for selectively ejecting ink.
Inkjet printing systems frequently make use of an inkjet printhead mounted to a carriage which is moved back and forth across print media such as paper. As the printhead is moved across the print media, a control device selectively activates each of a plurality of drop generators within the printhead to eject or deposit ink droplets onto the print media to form images and text characters. An ink supply that is either carried with the printhead or remote from the printhead provides ink for replenishing the plurality of drop generators.
Individual drop generators are selectively activated by the use of an activation signal that is provided by the printing system to the printhead. In the case of thermal inkjet printing, each drop generator is activated by passing an electric current through a resistive element such as a resistor. In response to the electric current the resistor produces heat, that in turn, heats ink in a vaporization chamber adjacent the resistor. Once the ink reaches vaporization, a rapidly expanding vapor front forces ink within the vaporization chamber through an adjacent orifice or nozzle. Ink droplets ejected from the nozzles are deposited on print media to accomplish printing.
The electric current is frequently provided to individual resistors or drop generators by a switching device such as a field effect transistor (FET). The switching device is activated by a control signal that is provided to the control terminal of the switching device. Once activated the switching device enables the electric current to pass to the selected resistor. The electric current or drive current provided to each resistor is sometimes referred to as a drive current signal. The control signal for selectively activating the switching device associated with each resistor is sometimes referred to as an address signal.
In one previously used arrangement, a switching transistor is connected in series with each resistor. When active, the switching transistor allows a drive current to pass through each of the resistor and switching transistor. The resistor and switching transistor together form a drop generator. A plurality of these drop generators are then arranged in a logical two-dimensional array of drop generators having rows and columns. Each column of drop generators in the array are connected to a different source of drive current and with each drop generator within each column connected in a parallel connection between the source of drive current for that column. Each row of drop generators within the array is connected to a different address signal with each drop generator within each row connected to a common source of address signals for that row of drop generators. In this manner, any individual drop generator within the two-dimensional array of drop generators can be individually activated by activating the address signal corresponding to the drop generator of row and providing drive current from the source of drive current associated with the drop generator column. In this manner, the number of electrical interconnects required for the printhead is greatly reduced over providing drive and control signals for each individual drop generator associated with the printhead.
While the row and column addressing scheme previously discussed is capable of being implemented in relatively simple and relatively inexpensive technology tending to reduce printhead manufacturing costs, this technique suffers from the disadvantage of requiring relatively large number of bond pads for printheads having large numbers of drop generators. For printheads having in excess of three hundred drop generators, a number of bond pads tends to become a limiting factor when attempting to minimize the die size.
Another technique that has been previously been used makes use of transferring activation information to the printhead in a serial format. This drop generator activation information is rearranged using shift registers so that the proper drop generators can be activated. This technique, while greatly reducing the number of electrical interconnects, tends to require various logic functions as well as static memory elements. Printheads having various logic functions and memory elements require suitable technologies such as CMOS technology and tend to require a constant power supply. Printheads formed using CMOS technology, which tend to be more costly to manufacturer than printheads using NMOS technology. The CMOS manufacturing process is a more complex manufacturing process than the NMOS manufacturing process that requires more masking steps that tend to increase the costs of the printhead. In addition, the requirement of a constant power supply tends to increase the cost of the printing device that must supply this constant power supply voltage to the printhead.
There is an ever present need for inkjet printheads that have fewer electrical interconnects between the printhead and the printing device thereby tending to reduce the overall costs of the printing system as well as the printhead itself. These printheads should be capable of being manufactured using a relatively inexpensive manufacturing technology that allows the printheads to be manufactured using high volume manufacturing techniques and have relatively low manufacturing costs. These printheads should allow information to be transferred between the printing device and the printhead in a reliable manner thereby allowing high print quality as well as reliable operation. Finally, these printheads should be capable of supporting large numbers of drop generators to provide printing systems that are capable of providing high print rates.
One aspect of the present invention is an inkjet printhead having a plurality of drop generators that selectively eject ink in response to activation. The inkjet printhead includes first and second drop generators disposed on the printhead. Each of the first and second drop generators are configured for connection to a source of drive current. The inkjet printhead also includes a control device configured for connection to a periodic address signal and first and second periodic enable signals. The control device is responsive to the first periodic enable signal and periodic address signal for enabling the first drop generator for activation in response to drive current. The control device is responsive to the second periodic enable signal and periodic address signal for enabling the second drop generator for activation in response to drive current.
In one preferred embodiment, the control device is a first and second control device with the first control device associated with the first drop generator and the second control device associated with the second drop generator.
Another aspect of the present invention is an inkjet printhead having a plurality of drop generators that selectively eject ink in response to activation. The inkjet printhead includes a pair of drive current contacts configured for connection to a source of drive current. Also included is a plurality of address contacts configured for connection to a corresponding plurality of sources of address signals. The plurality of address signals provides a repeating pattern of address signals with only one of the plurality of address signals active at a time and with the plurality of address signals each having a frequency of f. The inkjet printhead further includes first and second enable contacts that are configured for connection to a source of first and second periodic enable signals. Each of the first and second enable signals have an activation frequency of greater than f and only one of the first and second enable signals are active at a time. The plurality of drop generators are configured so that only a single drop generator of the plurality of drop generators is enabled for activation based on the signals at the first and second enable contacts and the signals at the plurality of address contacts. Each of the plurality of drop generators are activated if enabled and drive current is provided at the drive current contacts.
In one preferred embodiment, the plurality of address contacts is n and wherein each of the first and second enable signals has an activation frequency that is greater than (2xc3x97n)f.